ST1.8

To date, the inner boundary conditions for solar wind models are either directly or indirectly based on magnetic field extrapolation models of the photosphere. Furthermore, between the photosphere and Earth, there are no other direct empirical constraints on models. New breakthroughs in coronal rotation tomography, applied to coronagraph observations, allow maps of the coronal electron density to be made in the heliocentric height range 4-12 solar radii (Rs). We show that these maps (i) give a new empirical boundary condition for solar wind structure at a height where the coronal magnetic field has become radial, thus avoiding the need to model the complex inner coronal magnetic field, and (ii) give accurate rotation rates for the corona, of crucial importance to the accuracy of solar wind models and forecasts.

How to cite: Morgan, H.: Empirical inner boundary conditions and rotation rates for solar wind models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-782, https://doi.org/10.5194/egusphere-egu21-782, 2021.

In this work, the Dynamic Time Warping (DTW) technique is presented as an alternative method to assess the performance of modeled solar wind time series at Earth (or at any other point in the heliosphere). This method can quantify how similar two time series are by providing a temporal alignment between them, in an optimal way and under certain restrictions. It eventually estimates the optimal alignment between an observed and a modeled series, which we call the warping path, by providing a single number, the so-called DTW cost. A description on the reasons why DTW should be applied as a metric for the assessment of solar wind time series, is presented. Furthermore, examples on how exactly the technique is applied to our modeled solar wind datasets with EUHFORIA, are shown and discussed.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870437 (SafeSpace).

How to cite: Samara, E., Chane, E., Laperre, B., Verbeke, C., Temmer, M., Rodriguez, L., Magdalenic, J., and Poedts, S.: The Dynamic Time Warping as a means to assess modeled solar wind time series, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12459, https://doi.org/10.5194/egusphere-egu21-12459, 2021.

In this study we present a method for forecasting the ambient solar wind at L1 from coronal magnetic models. Ambient solar wind flows in interplanetary space determine how solar storms evolve through the heliosphere before reaching Earth, and accurately modelling and forecasting the ambient solar wind flow is therefore imperative to space weather awareness. We describe a novel machine learning approach in which solutions from models of the solar corona based on 12 different ADAPT magnetic maps are used to output the solar wind conditions some days later at the Earth. A feature analysis is carried out to determine which input variables are most important. The results of the forecasting model are compared to observations and existing models for one whole solar cycle in a comprehensive validation analysis. We find that the new model outperforms existing models and 27-day persistence in almost all metrics. The final model discussed here represents an extremely fast, well-validated and open-source approach to the forecasting of ambient solar wind at Earth, and is specifically well-suited for ensemble modelling or for application with other coronal models.

How to cite: Bailey, R., Reiss, M. A., Möstl, C., Arge, C. N., Henney, C., Owens, M., Amerstorfer, U., Amerstorfer, T., Weiss, A., and Hinterreiter, J.: Using Gradient Boosting Regressors to forecast the ambient solar wind from coronal magnetic models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15803, https://doi.org/10.5194/egusphere-egu21-15803, 2021.

We use the multi-year open acees database of current sheets identified at 1 AU with the one-second resolution from ACE data (https://csdb.izmiran.ru ) to study properties of current sheets in the solar wind. We find that the CS daily rate (the number of CSs per day) R correlates with the solar wind temperature T rather than with the solar wind speed V and is proportional to the sum of the kinetic and thermal energy density. The main statistical results preliminary obtained in the study are as follows:

• There is clustering of CSs.
• Maxima of R are associated with stream/corotating interaction regions (SIRs/CIRs) and interplanetary mass ejection (ICME) sheaths.
• On average, one-three thousands of CSs are detected daily at the Earth’s orbit. The best-fit parameter is (V ² (N+5 N ' ) + 10( N+ N ' )T )/5000 if V is given in km/s, T - in K, N is given in cm^-3,  and N ' =2 cm^-3 is the background level of the solar wind density. The correlation coefficient between the parameter and R  is ~0.8.
• There is no obvious connection between the daily CS rate and the solar cycle. However, this preliminary conclusion should be reconsidered after the expansion of the CS database to several solar cycles.

O.K. and R.K. are supported by Russian Science Foundation grant No. 20-42-04418. T.S. acknowledges the HSE’s general support and encouragement of student’s scientific activity.

How to cite: Khabarova, O., Sagitov, T., Kislov, R., and Li, G.: Multi-year statistical analysis of properties of current sheets at 1 AU, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13510, https://doi.org/10.5194/egusphere-egu21-13510, 2021.

Characterizing the detailed structure of the magnetic field in the active corona is of crucial importance for determining the chain of events from the formation to the destabilisation and subsequent eruption and propagation of coronal structures in the heliosphere. A comprehensive methodology to address these dynamic processes is needed in order to advance our capabilities to predict the properties of coronal mass ejections (CMEs) in interplanetary space and thereby for increasing the accuracy of space weather predictions. A promising toolset to provide the key missing information on the magnetic structure of CMEs are time-dependent data-driven simulations of active region magnetic fields. This methodology permits self-consistent modeling of the evolution of the coronal magnetic field from the emergence of flux to the birth of the eruption and beyond. 

In this presentation, we discuss our modeling efforts in which time-dependent data-driven coronal modeling together with heliospheric physics-based modeling are employed to study and characterize CMEs, in particular their magnetic structure, at various stages in their evolution from the Sun to Earth. 

How to cite: Pomoell, J., Kilpua, E., Price, D., Asvestari, E., Sarkar, R., Good, S., Kumari, A., Pal, S., and Daei, F.: Modeling the magnetic structure of CMEs in the inner heliosphere based on data-driven time-dependent simulations of active region evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13048, https://doi.org/10.5194/egusphere-egu21-13048, 2021.

How to cite: Lynch, B.: A Model for Coronal Inflows and In/Out Pairs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10416, https://doi.org/10.5194/egusphere-egu21-10416, 2021.

Using combined STEREO-SOHO white-light data, we present a method to determine the volume and density of a coronal mass ejection (CME) by applying the graduated cylindrical shell model (GCS) and deprojected mass derivation. Under the assumption that the CME  mass is roughly equally distributed within a specific volume, we expand the CME self-similarly and calculate the CME density for distances close to the Sun (15–30 Rs) and at 1 AU. The procedure is applied on a sample of 29 well-observed CMEs and compared to their interplanetary counterparts (ICMEs). Specific trends are derived comparing calculated and in-situ measured proton densities at 1 AU, though large uncertainties are revealed due to the unknown mass and geometry evolution: i) a moderate correlation for the magnetic structure having a mass that stays rather constant and ii) a weak correlation for the sheath density by assuming the sheath region is an extra mass - as expected for a mass pile-up process - that is in its amount comparable to the initial CME deprojected mass. High correlations are derived between in-situ measured sheath density and the solar wind density and solar wind speed as measured 24 hours ahead of the arrival of the disturbance. This gives additional confirmation that the sheath-plasma indeed stems from piled-up solar wind material. While the CME interplanetary propagation speed is not related to the sheath density, the size of the CME may play some role in how much material is piled up.

How to cite: Temmer, M., Holzknecht, L., Dumbovic, M., Vrsnak, B., Sachdeva, N., Heinemann, S. G., Dissauer, K., Scolini, C., Asvestari, E., Veronig, A. M., and Hofmeister, S.: Deriving CME volume and density from remote sensing data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2535, https://doi.org/10.5194/egusphere-egu21-2535, 2021.

The solar coronal magnetic field plays an important role in the formation, evolution, and dynamics of small and large-scale structures in the corona. Estimation of the coronal magnetic field, the ultimate driver of space weather, particularly in the ‘low’ and ‘middle’ corona, is presently limited due to practical difficulties. Data-driven time-dependent magnetofrictional modelling (TMFM) of active region magnetic fields has been proven as a tool to observe and study the corona. In this work, we present a detailed study of data-driven TMFM of active region 12473 to trace the early evolution of the flux rope related to the coronal mass ejection that occurred on 28 December 2015. Non-inductive electric field component in the photosphere is critical for energizing and introducing twist to the coronal magnetic field, thereby allowing unstable configurations to be formed. We estimate this component using an approach based on optimizing the injection of magnetic energy. We study the effects of these optimisation parameters on the data driven coronal simulations. By varying the free optimisation parameters, we explore the changes in flux rope formation and their early evolution, as well other parameters, e.g. axial flux, magnetic field magnitude.

How to cite: Kumari, A., Price, D., Kilpua, E., Pomoell, J., and Daei, F.: Effects of optimisation parameters on data-driven magnetofrictional modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9500, https://doi.org/10.5194/egusphere-egu21-9500, 2021.

Geomagnetic storms are mainly driven by the two main solar wind transients: coronal mass ejections (CME) and high-speed solar wind streams with related (corotating) stream interaction regions (HSS/SIR). CMEs are produced by new magnetic flux emerging on solar surface as active regions, and their occurrence follows the occurrence of sunspots quite closely. HSSs are produced by coronal holes, whose occurrence at the ecliptic is maximized in the declining phase of the solar cycle.

Geomagnetic storms are defined and quantified by the Dst index that measures the intensity of the ring current and is available since 1957. We have corrected some early errors in the Dst index and extended its time interval from 1932 onwards using the same stations as the Dst index (CTO preceding HER). This extended storm index is called the Dxt index. We have also constructed Dxt3 and Dxt2 indices from three/two of the longest-operating Dst stations to extend the storm index back to 1903, covering more than a century of storms.

We divide the storms into four intensity categories (weak, moderate, intense and major), and use the classification of solar wind by Richardson et al. into CME, HSS/SIR and slow wind -related flows in order to study the drivers of storms of each intensity category since 1964. We also correct and use the list of sudden storm commencements (SSC) collected by Father P. Mayaud, and divide the storms of each category into SSC-related storms and non-SSC storms.

Studying geomagnetic storms of different intensity category and SSC relation allows us to study the occurrence of CMEs and HSS/SIR over the last century. We also use these results to derive new information on the centennial evolution of the structure of solar magnetic fields.

How to cite: Mursula, K., Qvick, T., and Holappa, L.: A century of geomagnetic storms, CMEs and HSS/SIRs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13423, https://doi.org/10.5194/egusphere-egu21-13423, 2021.

We present a study of two CMEs observed at Mercury and 1 AU by spacecraft in longitudinal conjunction. Of the two CMEs, one propagated relatively self-similarly, while the other one underwent significant changes in its properties, making them excellent case studies to investigate the following question: what causes the drastic alterations observed in some CMEs during propagation, while other CMEs remain relatively unchanged? Answering this question will also help us better understand the potential impact of CMEs on the near-Earth environment. 

In this work we focus on the presence or absence of large-scale corotating structures in the propagation space between Mercury and 1 AU, that have been shown in the past to influence  the orientation  of  CME  magnetic  structures  and  the  properties  of  CME  sheaths. At both locations, we determine the CME flux rope orientation and characteristics using different fitting and classification methods. Our analysis is complemented by solar wind plasma measurements near 1 AU, by estimates of the size evolution of the sheaths and magnetic ejecta with heliocentric distance, and by the identification of solar wind structures in the CME propagation space based on in situ data, remote-sensing observations, and numerical simulations of the solar wind conditions in the inner heliosphere.

Results indicate that the changes observed in one CME were likely caused by a stream interaction region, while the CME exhibiting little change did not interact with any large-scale structure between Mercury and 1 AU. This work provides end-member examples of CME propagation in the inner heliosphere, exemplifying how interactions  with  corotating  structures  in  the  solar  wind  can  induce  essential  changes  in  CME structures. Our findings provide new fundamental insights on the propagation and evolution of CMEs, and can help lay the foundation for improved predictions of CME properties at 1 AU.

How to cite: Scolini, C., Winslow, R. M., Lugaz, N., and Galvin, A. B.: The effect of stream interaction regions on CME structures: observations in longitudinal conjunction at Mercury and 1 AU, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-661, https://doi.org/10.5194/egusphere-egu21-661, 2021.

Different regimes of the solar wind have been observed at L1 during and after the passage of ICMEs, particularly anomalies with very low plasma density. From the observations at L1 (ACE) we identified different possible cases. A first case was explained by the evacuation of the plasma due over expansion of the ICME (May 2002). The second case on July 2002 is intriguing.In July 2002, three halo fast speed ICMEs, with their origin in the central part of the Sun, have surprisingly a poor impact on the magnetosphere (Dst > -28 nT).   Analyzing the characteristics of the first ICME at L1, we conclude that the spacecraft crosses the ICME with a large impact (Bx component in GSE coordinates is dominant). The plasma density is low, just behind this first ICME. Next, we explore the generic conditions of low density formation in the EUHFORIA simulations.The very low density plasma after the sheath could be explained by the spacecraft crossing, on the side of the flux rope, while behind the front shock. We investigate two possible interpretations. The shock was able to compress and accelerate so much the plasma that a lower density is left behind. This can also be due to an effect of the sheath magnetic field which extends the flux rope  effect on the sides of it,    so a decrease of plasma density could occur like behind a moving object (here the sheath field). The following ICME, with also a low density, could be an intrinsic case with the formation in the corona of a cavity. Finally, we present some runs of EUHFORIA which fit approximately these data and argue in favor of the possible interpretations detailed above.

How to cite: Schmieder, B., Verbeke, C., Chané, E., Démoulin, P., Poedts, S., and Grison, B.: ICMEs and low plasma density in the solar wind observed at L1, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1799, https://doi.org/10.5194/egusphere-egu21-1799, 2021.

Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study developed a CME arrival-time forecasting system using a three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. The base MHD simulation is SUSANO-CME (Shiota and Kataoka 2016), in which CMEs are approximated as spheromaks. In the developed forecasting system, many MHD simulations with different CME initial speed are tested. The IPS responses of each MHD simulation run is calculated from the density distributions derived from the MHD simulation, and compared with IPS data observed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University. The CME arrival time of the simulation run that most closely agrees with the IPS data is automatically selected as the forecasted time.

We then validate the accuracy of this forecast using 12 halo CME events. The average absolute arrival-time error of the IPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereas that of MHD simulations without IPS data, in which the initial CME speed is derived from white-light coronagraph images, is approximately 6.7 h. This suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. The average predicted arrival times are earlier than the actual arrival times. These early predictions may be due to overestimation of the magnetic field included in the spheromak and/or underestimation of the drag force from the background solar wind, the latter of which could be related to underestimation of CME size or background solar wind density.

How to cite: Iwai, K., Shiota, D., Tokumaru, M., Fujiki, K., Den, M., and Kubo, Y.: Development and Validation of CME Arrival-Time Forecasting System by MHD Simulations based on Interplanetary Scintillation Observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3605, https://doi.org/10.5194/egusphere-egu21-3605, 2021.

Coronal mass ejections (CMEs), large scale transient eruptions observed in the Sun, are thought to also be spawned by other magnetically active stars. The magnetic flux ropes intrinsic to these storms, and associated high-speed plasma ejecta perturb planetary environments creating hazardous conditions. To understand the physics of CME impact and consequent perturbations in planetary environments, we use 3D compressible magnetohydrodynamic simulation of a star-planet module (CESSI-SPIM) developed at CESSI, IISER Kolkata based on the PLUTO code architecture.  We explore magnetohydrodynamic processes such as the formation of a bow-shock, magnetopause, magnetotail, planet-bound current sheets and atmospheric mass loss as a consequence of magnetic-storm-planetary interactions. Specifically, we utilize a realistic, twisted flux rope model for our CME, which leads to interesting dynamics related to helicity injection into the magnetosphere. Such studies will help us understand how energetic magnetic storms from host stars impact magnetospheres and atmospheres with implications for planetary and exoplanetary habitability.

How to cite: Roy, S. and Nandy, D.: Modelling the Impact of Magnetic Storms on Planetary Environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8863, https://doi.org/10.5194/egusphere-egu21-8863, 2021.

Coronal Mass Ejections (CMEs) and their interplanetary counterparts (ICMEs) are key drivers of space weather throughout the heliosphere. Observational studies are used to understand their evolution and for developing existing models and theory in space weather forecasting. Motivated by the future exploration of the solar high-latitudes by Solar Orbiter and complimented by Parker Solar Probe, we aim to contribute to the understanding of high-latitude CMEs as they develop into ICMEs. We examine a high-latitude CME and its subsequent ICME using data from STEREO, Ulysses, and near-Earth spacecraft. We apply a triangulation method to the remote-sensing images from the twin STEREO spacecraft and conduct a multi-spacecraft analysis using the in-situ Ulysses, STEREO, and near-Earth spacecraft data. The Ulysses observations, supported by the other spacecraft, provides a clear picture of the ICME geometry and structure: a shock, followed by a sheath region, and a magnetic flux rope followed by a high-speed stream. This ICME differs from the known ‘over-expanding’ types observed in the high-latitudes by the Ulysses mission, in that it straddles a region between the slow and fast solar winds which in itself drives a shock.

How to cite: Maunder, M., Foullon, C., Forsyth, R., Davies, E., Barnes, D., and Davies, J.: Multi-Spacecraft Observations of a Unique Type of High-Latitude ICME, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12295, https://doi.org/10.5194/egusphere-egu21-12295, 2021.